Aggregation behavior of surface active imidazolium ionic liquids in ethylammonium nitrate: effect of alkyl chain length, cations, and counterions.

The aggregation behavior of surface active imidazolium ionic liquids (ILs) with different alkyl chain length, cations, and counterions, namely, 1-alkyl-3-methylimidazolium bromide ([Cnmim]Br (n = 8, 10, 12)), 1-dodecyl-2,3-dimethylimidazolium bromide ([C12bmim]Br), 1-(2,4,6-trimethylphenyl)-3-dodecylimidazolium bromide ([C12pim]Br), and 1-dodecyl-3-methylimidazolium tetrafluoroborate ([C12mim][BF4]) in a protic room temperature IL, ethylammonium nitrate (EAN), was investigated through surface tension measurements and 1H NMR spectroscopy. Surface tension results show that surface properties and micellization behavior of surface active ILs in EAN are significantly affected by the structure of the cations, the basicity of counterions, and the hydrophobicity of alkyl chains. A detailed analysis of chemical shifts of various protons of surface active ILs and EAN was employed to investigate the micelle formation mechanism. Hydrogen bonding interaction is found to occur between the protons at C-2 on the imidazol...